Drilling rig control

ABSTRACT

THE OPERATION OF A DRILLING RIG IS MONITORED AND CONTROLLED TO PREVENT DAMAGE OR UNNECESSARY DELAY DUE TO THE OCCURRENCE OF OFF-NORMAL OPERATION. FOR EXAMPLE, DRILL STRING TWISTOFF MAY BE INDICATED BY A SUDDEN DECREASE IN THE TOTAL WEIGHT OF THE DRILL STRING, A SUDDEN DECREASE IN DRILLING TORQUE, OR A SUDDEN DECREASE IN MUD PUMP PRESSURE. EACH OF THESE THREE VARIABLES IN MONITORED, AND A DEPARTURE OF ANY ONE OF THE THREE FROM AN ESTABLISHED LEVEL MAY BE USED TO SOUND AN ALARM. A SUDDEN DECREASE IN THE DRILL STRING WEIGHT ACTUATES A CONTROL RELAT WHICH MAY SHUT DOWN THE DRILLING RIG OPERATION COMPLETELY, OR ANY PART THEREOF. A SUDDEN DECREASE IN DRILLING TORQUE AND/OR A SUDDEN DECREASE IN MUD PUMP PRESSURE SIMILARLY OPERATES A CONTROL RELATY TO SHUT DOWN THE DRILLING RIG OPERATION COMPLETELY, OR ANY PART THEREOF.

Sept. 20, 1971 J, BR-OMELL EI'AL 3,605,919

DRILLING RIG CONTROL Filed llav 16, 1969 6 .4 A I a 3 o 2 n 6 A a w v Q& 3 a u M 8 7 I- 4\ a 4 [\2 m m m o h. w 2 2 l p D 4 m +U O FIG. 2

United States Patent 01 Rice 3,605,919 Patented Sept. 20, 1971 US. Cl.175-27 Claims ABSTRACT OF THE DISCLOSURE The operation of a drilling rigis monitored and controlled to prevent damage or unnecessary delay dueto the occurrence of off-normal operation. For example, drill stringtwistoff may be indicated by a sudden decrease in the total weight ofthe drill string, a sudden decrease in drilling torque, or a suddendecrease in mud pump pressure. Each of these three variables inmonitored, and a departure of any one of the three from an establishedlevel may be used to sound an alarm. A sudden decrease in the drillstring weight actuates a control relay which may shut down the drillingrig operation completely, or any part thereof. A sudden decrease indrilling torque and/ or a sudden decrease in mud pump pressure similarlyoperates a control relay to shut down the drilling rig operationcompletely, or any part thereof.

BACKGROUND OF THE INVENTION This invention relates to drilling rigcontrol, and more particularly to a determination of off-normaloperation upon the deviation of one of three variables from individuallyestablished levels.

This invention also relates to a determination of drill string twistoffand to the detection of ledges and keyseats in a hole, and the controlof an automatic rig upon the detection of off-normal operation.

When drilling through a subsurface formation, many conditions candevelop which will cause off-normal operation of a drilling rig. One ofthe most serious malfunctions is the separation of the drill string intosections; this is commonly known as drill string twistoff. Once a drillstring has twisted off, additional operation of the drilling rig mayonly compound the troubles and delay the time before drilling can beresumed. In addition to drill string twistoff, other off-normaloperations that have caused serious damage and unnecessary delay includea sloughing shale condition, a dull or blocked drill bit, and holesdeveloping in the drill string. Each of these conditions, if notdetected and corrected early, may result in damage to the drilling rigitself.

Although only careful drilling procedures will prevent or minimize thepossibility of off-normal operation, a system in accordance with thepresent invention detects when a malfunction occurs such that immediateremedial action can be taken. Upon the occurrence of an offnormalcondition, the system sounds an alarm and, if appropriate controls areprovided, shuts down the drilling rig operation. The rig operators areimmediately aware of off-normal operation and can stage steps to correctthe malfunction and return to drilling with a minimum of down time.

In accordance with the present invention, transducers convert the drillstring weight into an electrical signal which is compared to a signalrepresenting a calculated drill string weight. If the electrical signaloutput of the transducer drops below the established signal in a setpoint controller, a relay coil is energized to close a series of relaycontacts, thereby sounding an alarm and shutting down the drilling rigoperation. Another transducer converts the pressure of the hydraulicmotors in the drill head into an electrical signal which is compared toeither a signal representative of formal drilling torque plus a marginof safe over-torque, or a signal representative of normal drillingtorque less a margin of safety. Any deviation of the output signal fromthe transducer above or below the established values will energize arelay coil. This relay coil operates contacts to sound an alarm and setup a condition to shut down the drilling rig operation upon theoccurrence of an unexpected decrease in mud pump pressure. The mud pumppressure is converted into an electrical signal for comparison to anestablished value of mud pump pressure. When the mud pump pressure fallsbelow or rises above the established value plus or minus a dead-band asa result of off-normal operation, a relay coil is energized to closecontacts which sound an alarm and shut down the drilling rig operation,assuming a sudden decrease in drilling torque has also occurred.

In accordance with a specific usage of the present invention, on ahydraulic drilling rig, forces supporting the drill head are monitoredas representing the drill string weight. Any appreciable decrease of themonitored force from an established level during the drilling operationis taken as an indication of drill string twistolf. The pressure at thehydraulic motors of the drill head is also monitored as representingdrilling torque. Again, an appreciable decrease of the monitoredpressure from an established value will be an indication of drill stringtwistoff. Mud pump pressure is also monitored as still another parameterthat may be used as an indication of drill string twistoff. Should themud pump pressure, during a drill cycle, suddenly decrease below anestablished value, there is a probability of drill string twistoff.

An object of the present invention is to provide automatic drilling rigoperation. Another object of the present invention is to provide anindication of off-normal drilling operation as a result of a drillstring weight change. A further object of this invention is to providefor automatically shutting down a drilling rig upon the detection of anapparent drill string weight change. Still another object of the presentinvention is to provide an indication of drill string twistoff upon asudden decrease in drill string weight. Yet another object of thisinvention is to provide an indication of off-normal drilling rigoperation upon the occurrence of a sudden increase or decrease indrilling torque. A still further object of this inveniton is to providean indication of off-normal operation of a drilling rig upon theoccurrence of a sudden increase or decrease in mud pump pressure.Another object is this invention is to provide an alarm system fordetecting when a drill string encounters a tight hole condition wheneither going into or coming out of a hole shaft.

A more complete understanding of the invention and its advantages willbe apparent from the following specification and claims and from theaccompanying drawings illustrative of the invention.

3 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of a drillingrig and three subsystems for detecting off-normal drilling operation;and

FIG. 2 is an electrical schematic of a system for indicating to a rigoperator an oil-normal operation and for shutting down a drilling rig.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, there isshown an applicationof the present invention to an automatic hydraulicdrilling rig of the type described in US. Patent No 3,156,213. Thedrilling rig includes a mast 12 withln Which is slidably carried avertically movable drill head assembly 14. Drill head assembly 14supports a drill string 16, only a portion of which has beenillustrated, that may be several thousand feet in length, by means ofelevators (not shown) or threaded coupling. Movement of the drill headassembly 14 relative to the mast 12 is accomplished by a suitably bracedtower 18 fixed to the top of the mast 12. The tower 18 includescylinders 20 and 22, more than two may be used, which are braced bystruts 24. Rods 26 and 28, which are mounted to pistons within thecylinders 20 and 22, respectively, effect vertical movement of the drillhead upon introduction of hydraulic fiuid into the cylinders throughpipes 30 and 32.

Fluid flow rates within the pipes 30 and 32 may be controlled by ahydraulic system of the type described in the copending United Statespatent application of Raymond J. Bromell et al., Ser. No. 782,231, filedDec. 9, 1968, and assigned to the assignee of the present inven tion. Asdescribed in this copending application, the yoke of a variabledisplacement pump is stroked to various positions to establish fiowrates in the pipes 30 and 32 and thus vary the speed of raising andlowering the drill head assembly 14. The pressure maintained in thecylinders 20 and 22 by the variable displacement pump will be at a levelestablished by the weight of the drill string 16.

Pressure transducers 34 and 36 are coupled to the pipes 30 and 32,respectively, and produce electrical signals proportional to the pipepressure. Since there are two or more cylinders lifting the drill headassembly 14 and drill string 16, a pressure in the pipes 30 and 32 willbe proportional to only a portion of the total weight of the drill headand drill string. Thus, the electrical signals from the transducers 34and 36 are added in a summing amplifier 38 to produce a signal on a line40 proportional to the weight of the drill string 16. The electricalsignal on the line 40 is coupled to an indicating meter 42. This meter42 has a scale 44 calibrated in drill string weight and a pointer 46 forindicating instantaneous drill string weight. In addition to the meter42, the signal on line 40 connects to a recorder 48 which produces apermanent record of drill string weight for further analysis.

In addition to generating electrical signals representing drill stringweight by converting pressure in the cylinders 20 and 22, othertransducers may be employed. For example, strain gauges may be mountedon the rods 26 and 28 to produce electrical signals representing thedrill string weight. Further, load cells may be mounted under the rig toproduce electrical signals that vary with drill string weight.

Of particular significance to the operation of the present invention,the signal on line 40 is tied to an alarm controller 50. A typicalcontroller 50 may include a potentiometer circuit coupled to a knob 52for establishing a signal representing the calculated weight of thedrill string 16. The alarm controller may also include an amplifierhaving a first output when the drill string weight is above a calculatedvalue, a second output when the actual weight is at the calculatedvalue, and a third output when the actual weight is below the calculated'value. The first and third outputs of the amplifier energize a relay 54to complete various alarm circuits and shut down the drilling rigoperation, as will be described shortly. When the first output energizesthe relay 54, a high alarm condition exists such as would occur when areduced hole, sloughing shale or keyseat is encountered when removingthe drill string from a hole. Energizing the relay 54 from the thirdoutput indicates a low alarm condition such as would occur for a drillstring t-wistoff or when encountering a ledge or bridge when loweringthe drill string into a hole.

A signal on line 40 is also coupled to a rate amplifier 56 whichenergizes the relay 54 when the rate of change of the drill stringweight exceeds an established level. Many rate amplifier circuits areavailable and additional description is not deemed necessary.

To indicate ofiF-normal drilling rig operation with the weight alarmcircuit described above, the knob 52 is set at a drill string weightcalculated to be slightly less than then weight being supported.Pressure in the pipes 30 and 32 will be maintained at a level to supportthe drill string and will remain at some reasonably constant value for agiven weight. Assume the drill string 16 is about two thousand feet longand a twistolf occurs at about the one thousand foot level, then thepressure in pipes 30 and 32 will be readjusted by means of automaticcontrols (not shown) to support the new weight and prevent the drillhead assembly from running to the top of and damaging the tower. A lowerpressure in the pipes 30 and 32 produces a signal of lower magnitude onthe line 40 that will be less than a signal established by the knob 52.As a result, the alarm controller 50 energizes the relay 54, therebyclosing a contact 54-1 in series with an indicating light 60 shown inFIG. 2. The light 60 will be connected to a source of voltage at theterminals 62 and 64 through a contact 66. The contact 66 has previouslybeen closed in the normal sequence of operation. In addition to turningon the light 60 by closing the contact 54-1, energizing the relay 54closes a contact 54-2 to energize a horn 68 to produce an audible alarm.

In addition to giving a visual and audible indication of a change indrill string weight, energizing the relay 54 also opens a contact 54-3which de-energizes a relay 70, thereby shutting down the drilling rig.The relay 70 is energized at the start of the drilling operation byclosing the switch 71 and pushing the reset button 74. This completes acircuit to the terminals 62 and 64 through a normally closed contact66-2. Contact 66-2 is opened after the sequence of activating thedrilling rig has been completed. The relay 70 will be energized throughother normally closed contacts, to be described. Energizing the relay 70closes contacts 70-1 and 7 0-2. Contact 70-1 completes a holding circuitfor the relay 70 and the contact 70-2 connects drilling rig controlcircuitry 72 to the terminals 62 and 64.

For the alarm controller 50 to properly control the relay 54, the knob52 must be adjusted for each additional length of drill pipe added tothe drill string 16. This can be accomplished by hand or automaticallyby a computer. However, should adjustment of the knob 52 be overlooked,the weight alarm circuitry Will give an indication of ofi" normal rigoperation by means of the rate amplifier 56. The rate amplifier 56energizes the relay 54 when the rate of change of drill string weightexceeds an estab lished value. Under normal operating conditions for thedrilling rig, that is, during the drilling operation or when loweringthe drill string into a hole, the rate of change will be below theestablished level. When a drill string twistoff or other malfunctionoccurs, however, the rate of change of drill string weight will be high,thereby energizing the relay 54. Energizing the relay 54- closescontacts 54-1 and 54-2 to activate the light 60 and the horn 68,respectively. In addition, energizing the relay 54 opens a contact 54-3,thereby de-energizing the relay 70. This, as explained, shuts down thedrilling rig operation.

In addition to indicating drill string twistoif, the weight alarmcircuitry will indicate a ledge condition before any damagng amount ofweight has been applied to a drill bit when lowering a string into apreviously formed hole. The knob 52 is set, by hand or automatically, ata drill string weight slightly lower than the pickup weight, that is,the hanging weight of the string. If the drilling bit comes in contactwith a ledge, the pressure in the pipes 30 and 32 will suddenlydecrease, thereby setting up the same conditions that were describedpreviously with regard to a twistofl. The light 60 and the horn 68 willbe activated and the relay 70 de-energized to shut down the drillingrig, thus preventing bending of the drill string and damage to the drillbit. This additional feature of the weight control circuitry shuts downthe rig before an excessive amount of weight damages the drill string orthe drill bit.

Still another feature of the weight alarm circuitry, the drilling rigwill be shut down before the drill bit binds in a tight hole or keyseatwhen removing the drill string from a hole. For this feature, the knob52 is set at a drill string weight slightly higher than the pickupweight of the string. The setting of the knob 52 should not, however, beat a level such that they relay 54 will be energized. A tight hole orkeyseat condition will be detected when removing the drill string by thethigh alarm (the third output) signal from the controller 50 whichenergizes the relay 54. As the drill bit encounters a keyseat or tighthole, the pressure in the pipes 30 and 32 will rapidly increase, therebygenerating the high alarm signal from the controller 50. Energizing therelay 54 will activate the light 60 and the horn 68 by closing contacts541 and 54-2, respectively. The relay 70 will be de-energized by openingthe contact 54-3 to shut down the rig, thus minimizing the possibilityof pulling the drill string in two or collapsing the mast.

Another variable that provides an indication of offnormal drilling rigoperation is the torque required to rotate the drill string. The drillhead assembly 14 includes one or more fluid motors 73 coupled throughpinion and gear mechanisms to a pipe gripper section 76. A completedescription of the drill head assembly 14 will be found in the U.S. Pat.No. 3,158,213. Hydraulic fluid for operating the motors 73 will beprovided through flexible hoses, such as the input hose 78 and thereturn hose 79. The torque alarm circuit includes a transducer 80 forconverting the pressure in the hose 78 to an electrical signal on a line82. The signal on line 82 therefore represents the pressure in the hose78 and in turn the torque produced by the hydraulic motor 73. The signalon line 82 is coupled to an indicating meter 84 having a scale 86calibrated in units of torque. A recorder 88 also connects to the line82 and produces a permanent record of the torque required for rotatingthe drill string 16.

To indicate an off-normal operation, e.g., a probability of drill stringtwistofl, the signal on line 82 connects to an alarm controller 90 whichmay include an amplifier having a first output when the signal on line82 is above a minimum setting and a second output when this signal dropsbelow the setting. The alarm controller 90 includes a knob 92, which maybe set by a computer, for setting a minimum and maximum value of torqueto be developed by the hydraulic motor 73. Any change in torque producedby the motors 73 above or below the setting on controller 90 willenergize a relay 94.

Energizing the relay 94 closes a contact 94-1 to connect a light 95 tothe terminals 62 and 64, Energizing the relay 94 also closes a contact94-2 and opens a contact 94-3 in the circuit for the horn 68 and relay70, respectively. Note, closing the contact 94-2 does not activate thehorn 68 and opening the contact 94-3 does not deenergize the relay 70.Since a decrease in torque is not a positive indication of a drillstring twistotf with the system illustrated, only the light 96 is turnedon to indicate to the operator a probable twistofl or that some othermalfunction has occurred.

In addition to indicating a drill string twistoff, a change in torquemay also indicate a dull drill bit. As the drill bit wears with usage,additional torque will be required to penetrate the subsurface layers.When this increase in torque exceeds the value set by the knob 92, therelay 94 will be energized, thereby indicating an off-normal operation.

For a sudden decrease in torque to activate the horn 68 and de-energizethe relay 70, there must be an accompanying non-programmed decrease inmud pump pressure. Drilling mud may be pumped into the drill string 16via a mud tube 98 and a hollow portion of the section 76. A hose 100connects to the mud tube 98 and a mud pump (not shown). The mud pumppressure alarm circuit includes a transducer 102 connected in the hose100 to convert the mud pump pressure to an electrical signal on line104. Usually, the transducer 102 will be installed in an oil chamberwhich is separated from the drilling mud by a flexible diaphragm. Suchtransducers are readily available and additional description is notdeemed necessary.

The electrical signal representing mud pump pressure on the line 104connects to an indicator/ alarm meter 106 or to a controller, such ascontroller 90. An indicator/ alarm meter suitable for the system shownincludes an indicating needle 108 and a set point needle 110. When thesetwo needles coincide, they operate electrical contacts to energize arelay 112 from an electrical power source 114. Energizing the relay 112closes a contact 112-1, as shown in FIG. 2, to connect a light 116 tothe terminals 62 and 64. Energizing the relay 112 also closes a contact112-2 and opens a contact 112-3 for the horn 68 and the relay 70,respectively. Closing the contact 112-2 will not actuate the horn 68 andopening the contact 112-3 will not de-energize the relay 70 unless therelays 94 and 112 are energized at the same time. If the relays 94 and112 are energized together, then the contacts 94-2 and 112-2 will beclosed and the horn 68 will be energized to give an audible signal to anoperator that a drill string twistoff has occurred. Opening the contacts94-3 and 112-3 at the same time will disconnect the relay 70 from theterminals 62 and 64, thereby shutting down the drilling rig by openingthe contact 70-2.

By monitoring mud pump pressure, off-normal operations other than adrill string twistolf may be detected. For example, if the drill stringsdevelops holes, the drilling mud will be lost through these holes andthe mud pump pressure will drop. By substituting the controller for themeter 106, a high mud pump pressure will cause an energization of therelay 112. High mud pump pressure will result when the drill bit becomesplugged or when a sloughing shale condition develops. When a drill bithecomes plugged, it is important that the drilling be stopped to avoiddamaging the bit. Not all deviations of mud pump pressure from a normalsetting, however, require a complete shutdown of the rig operation. Infact, it may be desirable to continue the flow of drilling mud at somenominal value. In a sloughing shale condition, the mud pump pressurewill be reduced to avoid damage to the hole through fracturing byexcessive pressure, but some drilling mud flow is desirable to preventthe shale from packing around the drill string.

Although the circuit of FIG. 2 illustrates that a drill string weightchange is an indication of a drill string twistoff independent of theother variables, it should be understood that by modifying the contactarrangement, a twistoff indication may not be given unless there was achange in drill string weight accompanied by deviation of one of theother variables from their established levels. By various contactarrangements, an indication of drill string twistoif can be made to bedependent upon a deviation from established levels of any combination oftwo of the three variables described. Thus, it should be understood thatthe contact arrangement described illustrates only one embodiment and isnot intended as a limitation to the system shown.

In conventional drilling rigs, fluid pressures may not be available toconvert to electrical signals for representing the desired variables.For example, in a conventional rotary drilling rig, an electrical signalrepresenting drill string weight may be produced by a wire-line anchorconverting pull on the dead line to hydraulic pressure which may then beconverted by the transducer 34. Mechanical devices are also availablefor detecting changes in tension in the rotary drive chain of aconventional rig. These mechanical devices include transducers forconverting rotary drive chain tension into electrical signalsrepresenting drilling torque. On electrically driven conventional rigs,the torque pickup may be a device for generating an electrical signalproportional to the electric current supplied to the rotary table drivemotors.

While only one embodiment of the invention, together with modificationsthereof, has been described in detail herein and shown in theaccompanying drawings, it will be evident that various furthermodifications are possible without departing from the scope of theinvention.

What is claimed is:

1. In a drilling rig having means for raising and lowering a drillstring, means for rotating the drill string and circuitry forcontrolling the operations of the means for raising, lowering androtating the drill string, a system for detecting off-normal operation,comprising:

means for generating a signal proportional to the drill string weightboth during tripping of the drill string in and out of a borehole andduring the period the drill string is being rotated;

means coupled to said generating means for producing a weight alarmsignal when the drill string weight deviates from an established valueduring tripping; and

means responsive to the weight alarm signal for actuating the circuitrycontrolling the drill string raising and lowering means. 2. Theapparatus of claim 1, wherein the means coupled to said generating meansalso produces a weight alarm signal when the drill string weightdeviates from an established value during rotation of the drill string.

3. The drilling rig of claim 1, including: means associated with themeans for rotating the drill string for generating a torque signalproportional to the torque being applied to said drill string; and

means coupled to the torque signal generating means for producing atorque alarm signal when the drilling torque deviates from anestablished value.

4. A system in the operation of a drilling rig as set forth in claim 1,which rig additionally includes a mud pump and circuitry for controllingthe operation of the mud pump, and which system also includes:

means operably associated with the mud pump for generating a mud pumpsignal proportional to mud pump pressure; and

means coupled to the mud pump signal generating means for producing apump alarm signal when the mud pump pressure signal deviates from anestablished level.

5. In a drilling rig having means for raising and lowering a drillstring, means for rotating the drill string, a mud pump and circuitryfor controlling the operations of the drill string raising, lowering androtating means and the mud pump, a system for detecting off-normaloperations, including:

means operably associated with the drill string rotating means forgenerating a signal proportional to the torque being applied to thedrill String;

means coupled to said generating means for producing a torque alarmsignal when the drilling torque deviates from an established value;

means operably associated with the mud pump for generating a pump signalproportional to mud pump pressure;

means coupled to the pump signal generating means for producing a pumpalarm signal when the pump signal deviates from an established level;and

means responsive to the torque alarm signal and the mud alarm signal foractuating the circuitry controlling the drill string raising, loweringand rotating means and the mud pump.

6. The system of claim 5, including:

means for generating a signal proportional to the drill string weight;

means coupled to said generating means for producing a weight alarmsignal when the drill string weight deviates from an established value;and

means responsive to the weight alarm signal for actuating the circuitrycontrolling the drill string raising, lowering and rotating means andthe mud pump.

7. In a drilling rig having means for raising and lowering a drillstring comprising cylinders and means for supplying a hydraulic fluid tosaid cylinders for raising and lowering said drill string, means forrotating said drill string comprising a drill head and means forcirculating a hydraulic fluid through said drill head for rotation ofthe drill string, means for circulating fluid through the drill stringand circuit means for controlling the operation of the means forsupplying hydraulic fluid to said cylinders, the means for circulating ahydraulic fluid through said drill head and the means for circulatingfluid through the drill string, the improvement which comprises:

a first transducer for converting the hydraulic presssure in the drillstring raising and lowering cylinders into an electrical signalproportional to drill string weight while said drill string is rapidlymoving, as during insertion and removal of the drill string from aborehole and while said drill string is moving relatively slowly, asduring the period when the borehole is being drilled;

a controller coupled to the first transducer and responsive to the drillstring weight signal for producing a weight alarm signal when the drillstring weight signal deviates from an established value; and

control means responsive to the alarm signal for actuating the circuitmeans.

8. In a drilling rig having means for raising and lowering a drillstring comprising cylinders and means for supplying a hydraulic fluid tosaid cylinders for raising and lowering said drill string, means forrotating said drill string comprising a drill head and means forcirculating a hydraulic fluid through said drill head for rotation ofthe drill string, means for circulating fluid through the drill stringand circuit means for controlling the operation of the means forsupplying hydraulic fluid to said cylinders, the means for circulating ahydraulic fluid through said drill head and the means for circulatingfluid through the drill string, the improvement which comprises:

first transducer means for converting the hydraulic pressure at thedrill head into an electrical signal which is proportional to drillingtorque;

a first controller coupled to the first transducer means for producing asignal when the drilling torque signal deviates from established values;

second transducer means for converting the pressure of the fluid beingcirculated through the drill string into an electrical signal which isproportional to the fluid pressure;

a second controller coupled to the second transducer means for producinga signal when the fluid pressure signal deviates from establishedvalues; and

control means responsive to the signals from the first and secondcontrollers for actuating the circuit means when both signals arepresent.

9. The system of claim 8, including:

third transducer means for converting the hydraulic pressure in thedrill string raising and lowering cylinders into an electrical signalproportional to the drill string weight;

a third controller coupled to the third transducer means for producing asignal when the drill string weight deviates from an established value;and

control means responsive to the signal from the third controller foractuating the circuit means.

10. A system in the operation of a hydraulic drilling rig for detectingoff-normal operation as set forth in claim 9, including:

means responsive to the rate of change of drill string weight forproducing a weight alarm signal when the rate of change of the drillstring weight deviates from a preset value.

References Cited 1,891,329 12/1932 LeCompte et a1 17538X 10 2,298,22210/1942 McShane 73-151X 2,539,758 1/1951 Silverman et al. 17548X2,582,217 1/1952 OLeary 173-9 2,832,566 4/1958 Bielstein 1754O 3,324,7176/1967 Brooks et al. 17548X 3,461,978 8/1969 Whittle 175-27 FOREIGNPATENTS 1,194,182 5/1959 France 175-27 OTHER REFERENCES McGhee, ed.:Two-Man Crew Operates Hydraulic Rig. In Oil & Gas 1., Sept. 22, 1958,pp. 92, 94, 95, 97. 98.

IAN A. CALVERT, Primary Examiner U.S. Cl. X.R.

